It is known that analog signals having a strongly consistent nature such as, for example, speech signals can be coded after sampling in an efficient manner by consecutively carrying out a number of different transformations on consecutive segments of the signal which each have a particular time duration. One of the known transformations for this purpose is linear predictive coding (LPC), for an explanation of which a reference can be made to the book entitled "Digital Processing of Speech Signals" by L. R. Rabiner and R. W. Schafer; Prentice Hall, New Jersey; chapter 8 which chapter is hereby incorporated by reference into this specification. As stated, LPC is always used for signal segments having a particular time duration, in the case of speech signals, for example, 20 ms, and is considered as short-term coding. It is also known to make use not only of a short-term prediction but also of long-term prediction (LTP), in which a very efficient coding is obtained by a combination of these two techniques. The principle of LTP is described in Frequenz (Frequency), volume 42, no. 2-3, 1988; pages 85-93; P. Vary et al.: "Sprachcodec fur dass Europaische Funkfernsprechnetz" ("Speech Coder/Decoder for the European Radio Telephone Network").
In LTP, for a signal segment to be coded, a search is made for a segment with the greatest possible similarity in a signal period, preceding the said segment, having a particular duration. Then a signal which is representative of the difference between the segment to be coded and the found segment, and also a signal which is representative of the time duration which has elapsed since the found segment, is transmitted in coded form, which can result in an appreciable reduction of the information to be transmitted. Because the basic principle of LTP does not appear to result in all cases in finding a signal segment with optimum similarity, an improvement of the LTP principle has been proposed under the name HLTP (high-resolution LTP). A possible implementation of HLTP is described in Eurospeech 89, European Conference on Speech Communication and Technology, Paris, September 1989, in the article entitled "Pitch Prediction with Fractional Delays in CELP coding" by J. S. Marques et al., which is hereby incorporated by reference into this specification. In the case of HLTP, the chance that the signal segment with the greatest similarity is found is increased by an increase in the sampling frequency of the preceding signal period by means of interpolation. A draw-back of HLTP is, however, that, as will be explained in greater detail below, the complexity of the coding is much greater than in the case of LTP as a result of an appreciable increase in the number of operations.